It is known that certain aircraft comprise a stabilizing horizontal tail plane that can be adjusted in inclination. An adjustable horizontal tail plane such as this is, in the art, designated by one or other of the abbreviations PHR (standing for Plane Horizontal Réglable [i.e., adjustable]) or THS (standing for Trimmable Horizontal Stabilizer). Just like a fixed horizontal tail plane, an adjustable horizontal tail plane is provided with elevators forming the trailing edge of said adjustable horizontal tail plane.
An adjustable horizontal tail plane can be deflected in the nose-up or nose-down direction and it is used in certain flight phases. For example, during the landing of the aircraft, it is customary to nose-up deflect said adjustable horizontal tail plane through action of the pilot or of an automatic system, said elevators being in direct aerodynamic alignment with said tail plane and the value of the angle of deflection of the adjustable horizontal tail plane depending on several parameters of the aircraft, such as the longitudinal position of the center of gravity, the total weight on landing, the configuration of the leading edge slats and of the trailing edge flaps, the thrust, the speed at the moment of landing, etc.
This value of the angle of deflection is significant since it conditions the behavior of the airplane during the phase of the landing flare-out and of the making of contact of the aircraft with the ground.
After this making of contact of the aircraft with the ground, the elevators attached to the adjustable horizontal tail plane are controlled by the pilot of the aircraft so as to take, from their position in direct aerodynamic alignment with said tail plane, a position in the nose-down direction so as to tilt down, about the main landing gear, the nose of said aircraft rolling over the ground. Thus, the front gear (which is located under the nose) may, in its turn, make contact with the ground.
It may happen that, under certain conditions of the aircraft and/or of the outside environment, the elevators do not have sufficient authority to make the nose of the aircraft tilt rapidly downwards, so that the latter rolls over the ground for some time with its nose raised and the front gear not in contact with the ground, thereby causing a delay in braking.